With a little exploration, wouldn't supplies be essentially unlimited? Certain
supplies wouldn't - types of food - but they could be supplemented with
vitamins and foods that purely provide a certain essential nutrient - e.g.
beef jerky for protein.
How much food, etc was available would depend a great deal on how many people survived and for how long. It's not explicitly clear in the show, but based on things people have said, it sounds like the apocalypse hit quickly. Maybe a few months?
As cde said, a lot of the packaged food will go bad relatively quickly (especially without electricity to keep the fridges going.) Canned food will survive, and has - it seems to make up the bulk of their scavenged supplies these days. However, just because it's out there doesn't mean our heroes will be rolling in it all day long - they still have to go out and get it, which is no small feat these days.
Why not get more tanks and things? These wouldn't be easy to find, but they'd
be worth looking for.
I expect they'd be easy enough to find if you know where the local military bases are, however, as was already said, they are not cheap on the gas. They also move slowly and make a LOT of noise, so trying to drive one home will bring a horde of zombies along with it. Also, if YOU know where to find them, so does everyone else who might be thinking the same thing. You might be walking directly into a fight you don't need to have, over a resource that you can honestly do just fine without.
And then you'll have to scavenge and transport the ammunition for the tank's gun, which is even bigger and heavier than other supplies you need more desperately, like food.
Finally, ask yourself: how useful is a tank - REALLY - in the zombie apocalypse?
You don't NEED a gun that big to kill zombies - in fact, firing it off will likely attract MORE zombies from miles around. Even against other survivors, you don't really need that kind of firepower unless they're entrenched behind some serious walls or they have a tank of their own. Plus, just having a tank will put a target on your backs from every rag-tag group of survivors who see you with it. They'll either want to steal the tank for themselves or they'll want to kill you just to "eliminate the threat."
Using conventional rifles or knives and blades - as they do in the show - is more effective in the long run. It's quieter vs zombies, less resource intensive while still providing enough force to get the job done, and helps you keep a low profile when dealing with other survivors.
Failing #2; why not soup up some vehicles better - find an RV dealer, or a
hummer dealer - a little work and you could mount machine guns - etc.
This is certainly plausible. As to why they haven't done it in the show, well, they've spent most of their time out in the boonies, away from the city where one is likely to find such things, on account of all the zombies. But for a different group in a different location, this might be something worth doing.
Machine guns may be overkill (see tanks, above) but certainly fortifying an RV and adding spikes and stuff could be useful. Then again, our heroes have sort of done this outside AFZ anyway.
Why not spend all free available time either building better security - or
searching out more secure outposts
This is, in large part, exactly what they have been doing. Searching for a good place to settle down, with good defenses and available renewable resources. They can't just BUILD a fortress - that requires metalworking, stoneworking, a whole litany of crafting skills, engineering knowledge and machinery they don't have, plus manpower and time to boot.
They had a good thing going in the prison, until the Gov tore it down and poured all sorts of zombies in. Now they've got Alexandria, which has some mighty fine walls and defensive structures, all things considered.
given some serious effort, a trap for Neagan and posse could end their
I don't know about "easily." I mean, this is essentially what they THOUGHT they were doing in the latter half of season 6, ambushing the facility Hilltop pointed them at. Unfortunately, Neagan's "posse" turned out to be a hell of a lot bigger than they had ever anticipated.
I wouldn't say they failed due to not taking the task seriously.
Even now, we don't know exactly how big Neagan's group is. Definitely more than 20 or 30 based on how many people they had roadblocking Hilltop. So how many do you think? 100? 1000? We have no idea how far their group stretches.
Setting "a trap" to take them all out before they know what hit them is going to be a tall order for the 20-something people left in AFZ. It's not a matter of "serious effort," it's a matter of logistics. I don't think Rick has enough people to take down the whole organization. Certainly not without first disrupting their communications network, which seems very advanced compared to everyone else we've seen so far.